1. Field of the Invention
The present invention relates generally to portable industrial ventilation fans. More particularly, my invention relates to a "snap together" heavy duty fan whose guards are stressed when fitted to the housing to reinforce the overall structure.
2. Description of the Prior Art
Fans that are capable of moving large volumes of high velocity air are used in many cooling applications. High velocity fans often provide the only cooling for workers in typical industrial plants. To practically control the effects of such cooling, it is desirable to control the direction, velocity, and volume of the air being driven. Often these fans are mishandled, dropped, or subjected to other damaging forces through carelessness and the like. The long term structural durability of such fans is of paramount importance.
I have previously proposed a fan that controls and directs air over long ranges. U.S. Pat. No. 5,480,282, issued on Jan. 2, 1996, and its teachings are hereby incorporated by reference. The prior art comprises many different fans. Most industrial designs use an elongated, tubular housing enclosing a multi-bladed fan driven at relatively high velocity. They are often referred to as "tube-axle" designs. Tube-axle fans have several advantages. They are durable and rugged. They are relatively uncomplicated and easy to build. However, such fans can be noisy and they tend to vibrate, with vibration intensity often increasing over time. Loud, continuous rattles are annoying and distracting. Further, vibration can eventually loosen critical parts causing misalignment or premature breakdown.
One cause of fan vibration relates to the drive belts employed with belt driven fans. Over time typical V-belts will eventually wear and deform. Thereafter the tension transmitted by the belt between the axis of rotation of the fan blades and the drive motor axis will vary in response to rotation. An annoying oscillating effect can result. The resultant vibration causes fan shaking and noise. Direct drive motors may ameliorate the problem of worn or distorted drive belts, but such motors are costly, and they present other problems.
"Tube-axle" fans often have their housing edges reinforced with a structural angle. Alternatively they may have a simple angle fluted or rolled into the material at the edge of each housing end. These reinforced edges lend rigidity to the housing and provide an anchor for the necessary safety guards that cover the blades. Typical guards are normally screwed or bolted to the housing edges using conventional, radially spaced apart fasteners (i.e., nuts and bolts). The fan design described in my aforementioned patent requires twenty four such fastener combinations for mounting the guards. Obviously this is reflected in the labor and material cost of production. Another disadvantage is that the fasteners may loosen and fall off over time in response to continued vibration. Further it has been found that such guard mounting techniques do not maximize structural integrity. Conventional guards screw-mounted through the normal procedure can eventually vibrate loose.
Several own prior art manufacturing processes may be used to fashion housing bodies with reinforced edges. However, known procedures inevitably entail expensive set-ups that make the changing of housing sizes difficult. Moreover, even though metal forming is a common procedure that works well to produce the housing body itself, subsequent rolling of the body into a desirable cylindrical housing shape is less precise. Since the desired cylindrical shape is difficult to achieve, distorted, somewhat non-circular ends result. Nonuniform tube ends make it difficult install conventional guards. Typical guards have an unyielding, circular shape that requires a consistent cylindrical housing for proper assembly. There are also numerous holes that must be properly aligned in the guard and the tube edge during assembly.
Furthermore, motor mounting brackets generally will not fit an out-of-round housing properly. As may well be imagined, difficulties shaping the housing body into a consistent cylindrical form and resultant guard and mounting bracket attachment problems may easily compromise the quality of the produced fan.
Another vexatious problem with conventional industrial fans involves structural deformation. Over time, internal stresses and dynamic forces generated during normal operation can misshape the fan, distorting the housing from the optimum round cross section. Many industrial fans are portable, and they are roughly moved about as necessary for spot cooling. Generally, such portable fans comprise external wheels mounted to the housing and a handle for conveniently pushing the fan to a desired location. Known prior art fans are not designed to maximize structural strength. They fail to adequately compensate for stresses exerted by the motors and other internal components upon the housing during movement. Their guards fail to make a maximum contribution to structural integrity.
Finally, a problem with conventional fan housings involves the numbers of components that must be handled during assembly and maintenance. Conventional guards and guard attachment devices require handling and installing several parts during manufacture as well as removing a corresponding number during routine maintenance. Also, most conventional mounting brackets use several components pieces that require considerable assembly time. Such brackets are often difficult to handle and store.